Apparatus and method for judging plastic

ABSTRACT

In a plastic identifying apparatus ( 1 ), a reference light (L 1 ) and a detecting light (L 2 ), each having a predetermined wavelength, are irradiated to an object to be identified ( 4 ), and the transmitted lights of the reference light (L 1 ) and detecting light (L 2 ) are received. A detecting value expressing the quantity of light received of the detecting light (L 2 ) is divided by a reference value expressing the quantity of light received of the reference light (L 1 ), to obtain a computed value, based on which performed is identification of plastic forming the object to be identified  4 . The wavelength of the reference light (L 1 ) is in a wavelength band (hereat, 1550 nm) in which the light absorptances of all the types of plastics are of the lowest level, and the wavelength of the detecting light (L 2 ) is in a wavelength region (hereat, in the range of 1700 to 1760 run) in which the absorption wavelength bands of many plastics except for PET, such as HDPE, are present.

TECHNICAL FIELD

This invention relates to a plastic identifying apparatus and a methodthereof to identified by what type of plastic the object to beidentified is formed.

BACKGROUND ART

In the recent years, the recycling of plastic products (especially PETbottles) has been proceeded. For efficient recycling, it is necessary toidentify and sort plastic products depending on the type of theirmaterial, and it is being a theme how to conduct the identification ofplastic products.

As a conventional plastic identifying apparatus using light, there isone in which near-infrared ray is irradiated to a plastic product whilecontinuously changing the wavelength in the wavelength region of 1 to2.5 μm, and the differential spectrum of its absorption spectrum isanalyzed to identify the type of plastic forming the plastic product.

However, since in this conventional identifying apparatus it isnecessary to irradiate near-infrared ray to plastic products whilecontinuously changing the wavelength in the wavelength region of 1 to2.5 μm, there is the problem that the optical system is complicated.Further, such a complicated processing of finding the differentialspectrum is also needed in a signal processing after light receiving,and there are the problem that the apparatus construction and signalprocessing are complicated, and the problem that identification istime-consuming.

In addition, as regards the light source in this case, an incandescentlamp and mercury lamp are usually employed as one which emitsnear-infrared ray having a wavelength region of 1 to 2.5 μm. Hence,there is the problem due to the lifetime of the light source that itsmaintenance is laborious and the apparatus cost is increased as a whole.

In this conventional technique, there is a method in which no scanningof wavelength on the light source side is performed and an irradiationlight having a wide wavelength region is irradiated from a light sourceand, when receiving the light, a wavelength selection is performed byusing a spectral device such as grating. However, the problem of thelight source lifetime is not solved, in addition to the fact that thecost is increased because the spectral device itself is extremelyexpensive.

DISCLOSURE OF INVENTION

It is a first object of this invention to provide a plastic identifyingapparatus and a method thereof which enable to simplify the apparatusstructure and signal processing and also attain a rapid identifyingprocessing.

It is a second object of this invention to provide a plastic identifyingapparatus and a method thereof, taking less time for maintenance.

Accordingly, in order to attain the above objects, this inventionprovides a plastic identifying apparatus (1, 21, 31, 41, 51) to identifyby what type of plastic in predetermined plural types an object made ofplastic to be identified (4) is formed, characterized by comprising alight source (2, 3, 3 a, 3 b) irradiating to said object to beidentified a detecting light (L2, L2 a, L2 b) of which wavelength is inan absorption wavelength band to increase the light absorptance of atleast one type of plastic in said plural types, and a reference light(L1) of which wavelength is different from said wavelength of saiddetecting light; a light receiving means (5, 5 a, 5 b, 5 c) receiving atransmitted light or reflected light of said reference light and saiddetecting light from said object to be identified, and outputting areference value expressing the quantity of light received of saidreference light and a detecting value expressing the quantity of lightreceived of said detecting light; and an identifying means (7) computinga proportion of or difference between said reference value and saiddetecting value, and identifying, based on the computed value, by whattype of plastic in said plural types said object to be identified isformed.

Also, in order to attain the above objects, this invention provides aplastic identifying method of identifying by what type of plastic inpredetermined plural types an object made of plastic to be identified(4) is formed, characterized by comprising the steps of: a lightirradiating step of irradiating to said object to be identified, by apredetermined light source, a detecting light (L2, L2 a, L2 b) of whichwavelength is in an absorption wavelength band to increase the lightabsorptance of at least one type of plastic in said plural types, and areference light (L1) of which wavelength is different from saidwavelength of said detecting light; a light receiving step of receivingby a predetermined light receiving means (5, 5 a, 5 b, 5 c) atransmitted light or reflected light of said reference light and saiddetecting light from said object to be identified, and outputting tosaid light receiving means a reference value expressing the quantity oflight received of said reference light and a detecting value expressingthe quantity of light received of said detecting light; and anidentifying step of computing a proportion of or difference between saidreference value and said detecting value, and identifying, based on thecomputed value, by what type of plastic in said plural types said objectto be identified is formed.

With this construction, it is unnecessary to scan the irradiation lightin a predetermined wavelength region, as has been conventional, so thatthe apparatus construction such as of optical system and the signalprocessing after light receiving can be simplified, and a rapididentification can be attained.

Further, it is so arranged as to compute a proportion of or differencebetween a reference value expressing the quantity of light received of areference light and a detecting value expressing the quantity of lightreceived of a detecting light, and then perform identification based onthe computed value. Therefore, the identification can be conducted byremoving the unnecessary variable factor that varies depending onfactors other than the type of plastic, for example, the shape of theobject to be identified or the surface state such as dirt and damage.This leads to accurate identification.

Furthermore, in the case that identification is conducted by using theproportion of a reference value and a detecting value, when obtainingthe proportion, the magnitude of the detecting value is standardized bythe reference value. Therefore, there is the advantage that withoutspecially standardizing the emission intensity and the like of areference light and detecting light of a light source, theidentification can be conducted irrespective of their settingconditions.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing a light transmission property of polyethyleneterephthalate (PET).

FIG. 2 is a graph showing a light transmission property of high-densitypolyethylene (HDPE).

FIG. 3 is a graph showing a light transmission property of polyvinylchloride (PVC).

FIG. 4 is a graph showing a light transmission property of low-densitypolyethylene (LDPE).

FIG. 5 is a graph showing a light transmission property of polypropylene(PP).

FIG. 6 is a graph showing a light transmission property of polystyrene(PS).

FIG. 7 is a graph showing a light transmission property ofpolyvinylidene chloride (PVDC).

FIG. 8 is a diagram obtained by superposing the graphs shown in FIGS. 1to 7, but showing in enlarged dimension the range of about 1650 to about1750 nm.

FIG. 9 is a diagram obtained by superposing the graphs shown in FIGS. 1to 7, but showing in enlarged dimension the range of about 1540 to about1560 nm.

FIG. 10 is a graph showing the magnitude of light transmittance of eachplastic at each wavelength when the light transmittance of each plasticat 1550 nm is taken as a reference (100%).

FIG. 11 is a diagram showing a construction of a plastic identifyingapparatus according to a first preferred embodiment of this invention.

FIG. 12 is a diagram showing a construction of a plastic identifyingapparatus according to a second preferred embodiment of this invention.

FIG. 13 is a diagram showing a modification of the plastic identifyingapparatus according to the first and second preferred embodiments.

FIG. 14 is a diagram showing another modification of the plasticidentifying apparatus according to the first preferred embodiment.

FIG. 15 is a diagram showing another modification of the plasticidentifying apparatus according to the second preferred embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION First Preferred Embodiment

Firstly, based on FIGS. 1 to 10, description will proceed to a lightabsorbing property of plastic that is an example of objects to beidentified, to which identification is conducted by a plasticidentifying apparatus according to this preferred embodiment.

In the graphs of FIGS. 1 to 9, the abscissa indicates the wavelength ofthe light that is allowed to enter each plastic, and the ordinateindicates the light transmittance of the light of each wavelength toeach plastic. That is, in the graphs of FIGS. 1 to 9, as the value ofthe ordinate of the graph is smaller, the light absorptance of eachplastic is increased.

As the graphs of FIGS. 1 to 8 show, it is found that the absorptionwavelength band in which the light absorptance of PET, HDPE, PVC, LDPE,PP, PS and PVDC falls within the infrared light region having a longerwavelength than 1600 nm. More specifically, the absorption wavelengthband of HDPE, PVC, LDPE, PP and PVC is in the range of 1700 to 1760 nm,and the absorption wavelength band of PET and PS is substantially in therange of 1640 to 1700 nm.

On the other hand, from the graphs of FIGS. 1 to 7 and 9, it is foundthat in the range of 1500 to 1600 nm, the light absorptance of PET,HDPE, PVC, LDPE, PP, PS and PVDC translates approximately flat atsubstantially the lowest level.

Thereby in the present preferred embodiment, the light of whichwavelength is in the range of 1500 to 1600 nm is used as a referencelight L1 serving as a reference (see FIG. 11). Also, the light of whichwavelength is in the range of 1700 to 1760 nm or 1640 to 1700 nm is usedas a detecting light L2 (see FIG. 11). The reference light L1 anddetecting light L2 are irradiated to an object made of plastic to beidentified (see FIG. 11), and the received light intensity of thetransmitted light or reflected light of the detecting light L2 from theobject 4 is divided by the received light intensity of the transmittedlight or reflected light of the detecting light L2 from the object 4and, based on the computed value thus obtained, the type of plasticforming the object 4 is identified.

Hereat, the graphs G1 c to G7 c of FIG. 10 indicate the magnitude of thelight transmittance of each plastic to each wavelength when the lighttransmittance of each plastic at 1550 nm is taken as a reference (100%).

A first preferred embodiment of this invention will next be describedbased on FIG. 11.

As shown in FIG. 11, the plastic identifying apparatus 1 comprises, asits main components, a semiconductor light-emitting device 2 irradiatinga reference light L1, a semiconductor light-emitting device 3irradiating a detecting light L2, a light receiving device (lightreceiving means) 5 receiving the reference light L1 and detecting lightL2 from an object to be identified 4, a storage part (storing means) 6,and a microprocessor (identifying means) 7. Hereat, the semiconductorlight-emitting devices 2 and 3 correspond to a light source according tothis invention. The object to be identified 4 is to be one which isformed by one of the seven types of plastics as described above.

A laser diode capable of emitting light at a narrow wavelength width isused for the semiconductor light-emitting elements 2 and 3, and anInGaAsP laser diode is used especially for the semiconductorlight-emitting device 3.

The semiconductor light-emitting device 2 irradiates the reference lightL1 of which wavelength is in the range of 1500 to 1600 nm, toward theobject to be identified 4. The peak wavelength of the reference light L1is set to about 1550 nm. The reference light L1 emitted by thesemiconductor light-emitting device 2 is irradiated via a dichroicmirror 8 and a lens 9 to the object to be identified 4. As the dichroicmirror 8, there is used one which selectively allows passage of lighthaving a wavelength of 1550 nm. Although the dichroic mirror 8 is usedherein as a means for efficiently interpose the optical axes of thereference light L1 and detecting light L2, other means such as a prismor grating may be used. Alternatively, only for the purpose ofinterposing the optical axis of the reference light L1 and the opticalaxis of the detecting light L2, a half mirror may be used instead of thedichroic mirror 8.

The semiconductor light-emitting device 3 irradiates the detecting lightL2 of which wavelength is in the range of 1700 to 1760 nm, toward theobject to be identified 4. The wavelength width of the detecting lightL2 is here set to the vicinity of 1715 to 1735 nm. The detecting lightL2 emitted by the semiconductor light-emitting device 3 is reflectedfrom the dichroic mirror 8 so that its optical axis matches the opticalaxis of the reference light L1, and then irradiated via the lens 9 tothe object to be identified 4.

These semiconductor light-emitting devices 2 and 3 are driven byprojector circuits 10 and 11, and are drivingly controlled by themicroprocessor 7 via the projector circuits 10 and 11.

The light receiving device 5 successively receives via a lens 12 thetransmitted light of the reference light L1 and detecting light L2 fromthe object to be identified 4, and outputs an electric signal indicatingthe output value according to the quantity of the light received. Theelectric signal outputted from the light receiving device 5 is inputtedto the microprocessor 7 via a light receiving circuit 13 and an A/Dconverting circuit 14. In the plastic identifying apparatus 1, it isarranged such that the reference light L1 and detecting light L2 aresuccessively emitted at different timings. In response to this, thelight receiving device 5 successively receives the transmitted light ofthe reference light L1 and detecting light L2 from the object to beidentified 4, and it successively outputs an electric signal indicatinga reference value corresponding to the quantity of light received of thereference light L1 and an electric signal indicating a detecting valuecorresponding to the quantity of light received of the detecting lightL2.

A plurality of reference values that respectively correspond to pluraltypes of plastics previously selected are stored in the storage part 6.Hereat, there are stored seven reference values that correspond to PET,HDPE, PVC, LDPE, PP, PS and PVDC, respectively.

In response to a distinguished command to be inputted via aninput/output circuit 15, the microprocessor 7 allows the semiconductorlight-emitting device 2 via the projector circuit 10 to light up in theform of pulses for a predetermined short time, thereafter, allows viathe projector circuit 11 the semiconductor light-emitting device 3 tolight up in the form of pulses for a predetermined short time, whilereading, via the light receiving circuit 13 and AID converting circuit14, the reference value and detecting value which are successivelyoutputted from the light receiving device 5 in synchronizationtherewith.

Then the microprocessor 7 divides the detecting value with the referencevalue and judges to which reference value in the plural reference valuesstored in the storage part 6 the computed value is the closest, therebyit is identified by which plastic in the above-mentioned seven typesplastics the object to be identified 4 is formed. That is, it is judgedthat the object to be identified 4 is formed by the plastic thatcorresponds to the reference value being the closest to the computedvalue in the plural reference values. The result of identification isoutputted to the exterior via the input/output circuit 15.

Hereat, it may be arranged such that in determining to which referencevalue the computed value is the closest, a plurality of reference rangescorresponding to their respective reference values are previouslyprovided and the closest reference value is determined by judging withinwhich reference range the computed value falls.

The plural reference values stored in the storage part 6 may employ theresult of measurement in another apparatus, alternatively, the result ofmeasurement in the plastic identifying apparatus 1.

In the case of employing the result of measurement in another apparatus,it is necessary to prepare a reference value and input it into theplastic identifying apparatus 1. This will be described in order.Firstly, by such another apparatus, a reference light L1 and a detectinglight L2 are irradiated in order toward a plurality of objects to beidentified 4 formed by the respective types of plastics, and thetransmitted light (or reflected light) of the reference light L1 anddetecting light L2 from the objects to be identified 4 are received,thereby obtaining a reference value and a detecting value expressing thequantity of the light received of the reference light L1 and detectinglight L2, respectively. The detecting value is then divided by theobtained reference value to prepare a plurality of reference values thatcorrespond to the respective types of plastics. The prepared pluralreference values are associated with the respective types of plasticsand then inputted via the input/output circuit 15 to the plasticidentifying apparatus 1. The inputted plural reference values areassociated with the respective types of plastics and then recorded inthe storage part 6 by the microprocessor 7.

Whereas in the case of employing the result of measurement in theplastic identifying apparatus 1 as a reference value, it is necessary toperform teaching to the plastic identifying apparatus 1. When performingthe teaching, it is necessary that the plastic identifying apparatus 1is switched from the normal mode for performing plastic identificationto a teaching mode by inputting a mode switching command via theinput/output circuit 15. This teaching is conducted as follows. Like theabove-mentioned plastic identifying case, by the plastic identifyingapparatus 1, a reference light L1 and a detecting light L2 areirradiated to objects to be identified 4 formed by the respective typesof plastics, to receive the transmitted light of the reference light L1and detecting light L2 from the objects to be identified 4, and thedetecting value corresponding to the detecting light L2 is divided bythe reference value corresponding to the reference light L1, to preparea plurality of reference values that correspond to the respective typesof plastics. The prepared plural reference values are associated withthe plural types of plastics and then stored in the storage part 6. Thereturn from the teaching mode to the normal mode is performed byinputting a return command via the input/output circuit 15. Such ateaching processing is performed by the control of the microprocessor 7.

The plastic identifying apparatus 1 thus constructed is installed on anidentifying processing line, etc., for identifying plastic products suchas of a recycling processing facility or the like, and is utilized foridentifying plastic products. In this case, the plastic identifyingapparatus 1 is connected to a central control unit controlling the line,so that it successively performs identifying processing in response toan identifying command provided from the central control unit, andsuccessively outputs the result of identification to the central controlunit.

Specifically, when an identifying command is provided from the centralcontrol unit to the plastic identifying apparatus 1, a reference lightL1 and a detecting light L2 are successively irradiated to the object tobe identified 4 by the semiconductor light-emitting devices 2 and 3, andthe transmitted light of the reference light L1 and detecting light L2from the object to be identified 4 are received by the light receivingdevice 5. Then, electric signals indicating a reference value expressingthe quantity of the light received of the reference light L1 and adetecting value expressing the quantity of the light received of thedetecting light L2 are inputted to the microprocessor 7 via the lightreceiving circuit 13 and A/D converting circuit 14.

By the microprocessor 7, the detecting value is divided by the referencevalue, and it is judged to which reference value of the plural referencevalues stored in the storage part 6 the computed value is the closest.Thereby, the type of plastic forming the object to be identified 4 isidentified and its result is outputted to the central control unit viathe input/output circuit 15.

As described above, according to this preferred embodiment, a referencelight L1 and a detecting light L2, each having a predeterminedwavelength, are irradiated to the object to be identified 4, and thetransmitted light of the reference light L1 and detecting light L2 fromthe object to be identified 4 are received to perform identification.Therefore, it is unnecessary to scan an irradiation light within apredetermined wavelength region, as has been conventional, so that theapparatus construction such as of optical system and the signalprocessing after light receiving can be simplified, and a rapididentification can be attained.

Further, the identification is conducted based on the value obtained bydividing the detecting value expressing the quantity of the lightreceived of the detecting light L2 by the reference value expressing thequantity of the light received of the reference light L1. Therefore, theidentification can be conducted by removing the unnecessary variablefactor that varies depending on factors other than the type of plastic,for example, the shape of the object to be identified 4 or the surfacestate such as dirt and damage. This enables to conduct accurateidentification.

The detecting value is divided by the reference value and the magnitudeof the detecting value is standardized by the reference value.Therefore, there is the advantage that without specially standardizingthe emission intensity and the like of the reference light L1 anddetecting light L2 of the semiconductor light-emitting devices 2 and 3,the identification can be conducted irrespective of their settingconditions.

Since in this preferred embodiment the semiconductor light-emittingdevices 2 and 3 having a long lifetime are used as a light source, it issubstantially unnecessary to replace the light source, thus requiringless time in maintenance.

Further, in this preferred embodiment, a semiconductor laser device isused for the semiconductor light-emitting devices 2 and 3. Since thesemiconductor laser device emits a light at a narrow wavelength width,the emitted light can be directly irradiated to the object to beidentified 4, without passing through a filter for wavelength selection.As a result, the light source construction can be simplified, and thewaste of energy consumption is avoidable.

Since the wavelength of the reference light L1 falls within a wavelengthregion in which all the types of the plastics in the above-mentionedseven types have the lowest level of light absorptance (hereat, in therange of 1500 to 1600 nm), it is able to increase a difference between areference value corresponding to the reference light L1 and a detectingvalue corresponding to the detecting light L2. Thereby, the computedvalue obtained by dividing the detecting value by the reference valuecan be changed at a large variable width according to the difference ofthe corresponding type of plastic, and the identification can beconducted easily and accurately.

In this preferred embodiment, the light of which peak wavelength isabout 1550 nm is used for the reference light L1. Since this wavelengthband is used for optical communication, there is the advantage that itis easy to purchase semiconductor light-emitting devices.

Further, the light of which wavelength is in the range of 1700 to 1760nm (hereat, the light of which wavelength width is in the vicinity of1715 to 1735 nm) is used for the detecting light L1. Since in thewavelength region of 1700 to 1760 nm, the absorption wavelength band ofHDPE, PVC, LDPE, PP and PVD are within the range of 1700 to 1760 nm, itis easy to identify PET and PS, of which absorption wavelength band doesnot fall within this wavelength region, from HDPE, PVC, LDPE, PP andPVDC.

Second Preferred Embodiment

A plastic identifying apparatus according to a second preferredembodiment will next be described based on FIG. 12. In the constructionof FIG. 12, the same reference numerals have been used for the partscorresponding to the construction of FIG. 11, and its description isomitted.

In a plastic identifying apparatus 21 according to this preferredembodiment, two semiconductor light-emitting devices 3 a and 3 b toirradiate detecting lights L2 a and L2 b having different wavelengths,respectively, are provided instead of the semiconductor light-emittingdevice 3 according to the first preferred embodiment. The semiconductorlight-emitting devices 3 a and 3 b are drivingly controlled by amicroprocessor 7 via projector circuits 11 a and 11 b. A semiconductorlaser device is used for the semiconductor light-emitting devices 3 aand 3 b.

The semiconductor light-emitting device 3 a is the same as thesemiconductor light-emitting device 3 of the first preferred embodiment,and it irradiates a first detecting light L2 a being the same as thedetecting light L2 of the first preferred embodiment, toward an objectto be identified 4.

In this preferred embodiment, along with the installation of thesemiconductor light-emitting device 3 b, a dichroic mirror 22 isdisposed between a dichroic mirror 8 and a lens 9. The reference lightL1 transmitted from the dichroic mirror 8 and the first detecting lightL2 a reflected from the dichroic mirror 8 are transmitted from thedichroic mirror 22 and then irradiated via the lens 9 to the object tobe identified 4.

The semiconductor light-emitting device 3 b irradiates a detecting lightL2 b of which wavelength is in the range of 1640 to 1700 nm to theobject to be identified 4. Hereat, the wavelength width of the detectinglight L2 b is set to the vicinity of 1650 to 1670 nm. The seconddetecting light L2 b emitted by the semiconductor light-emitting device3 b is reflected from the dichroic mirror 22 so that its optical axismatches the optical axes of the reference light L1 and the firstdetecting light L2 a, and is irradiated via the lens 9 to the object tobe identified 4.

A light receiving device 5 successively receives via a lens 12 thetransmitted light of the reference light L1 from the object to beidentified 4 and the transmitted light of the detecting lights L2 a andL2 b from the object to be identified 4, and then successively outputsan electric signal indicating a reference value expressing the quantityof the light received of the reference light L1, an electric signalindicating a first detecting value expressing the quantity of the lightreceived of the first detecting light L2 a, and an electric signalindicating a second detecting value expressing the quantity of the lightreceived of the second detecting light L2 b.

In a storage part 6, a plurality of reference values that respectivelycorrespond to plural types of plastics selected in advance, as shown inthe following Table 1 and Table 2, are associated with the respectivetypes of plastics and stored for each of the detecting lights L2 a andL2 b. A group of reference values shown in Table 1 corresponds to thefirst detecting light L2 a, and a group of reference values shown inTable 2 corresponds to the second detecting light L2 b.

TABLE 1 Type PET HDPE PVC LDPE PP PS PVDC Maximum 96.62 31.28 48.2227.21 35.26 53.14 68.78 Middle 92.02 29.8  45.92 25.91 33.58 50.6  65.51Minimum 87.42 28.31 43.62 24.62 31.9  48.07 62.23

TABLE 2 Type PET HDPE PVC LDPE PP PS PVDC Maximum 71.63 56.24 81.0981.54 90.83 37.72 82.56 Middle 68.22 53.56 77.23 77.66 86.5  35.92 78.63Minimum 64.81 50.88 73.37 73.78 82.18 34.12 74.7 

Hereat, seven groups of reference values that respectively correspond toPET, HDPE, PVC, LDPE, PP, PS and PVDC are previously stored for each ofthe detecting lights L2 a and L2 b. Each group of reference values ismade up of middle value, maximum value and minimum value. The maximumvalue and minimum value are, as will be described hereinafter, thosewhich indicate an allowance error range when a microprocessor 7 comparesthe computed values corresponding to the detecting lights L2 a and L2 b,respectively, with each reference value (hereat, each middle value),thereby performing plastic identification. Taking the middle value as areference, the maximum value and minimum value are set to a value ofplus or minus several % (hereat, plus or minus 5%) of the middle value.

It should be noted that in the allowance error ranges of the respectivetypes of plastics shown in Table 1, the allowance error range of PVC(43.62 to 48.22) and the allowance error range of PS (48.07 to 53.14)are partially overlapped with each other in the range of 48.07 to 48.22.This is because at the wavelength band of the first detecting light L2a, PVC and PS are similar to each other in light absorptance. It istherefore difficult to perform accurate identification between PVC andPS, only by the first detecting light L2 a.

Accordingly, in this preferred embodiment, as will be describedhereinafter, a first computed value obtained by dividing the firstdetecting value corresponding to the first detecting light L2 a by thereference value, falls within such a region in which a plurality ofallowance error ranges corresponding to the first detecting light L2 aare overlapped with each other (hereat, in the range of 48.07 to 48.22),no identification using the first computed value is performed withinthat region, but the identification is performed by using a secondcomputed value obtained by dividing the second detecting valuecorresponding to the second detecting light L2 b by the reference value.

Although in this preferred embodiment the allowance error range is setto plus or minus 5% of the middle value, thus causing such overlappingof the allowance error range, the above-mentioned seven types ofplastics may be capable of being identified only by the first detectinglight L2 a, by increasing the accuracy of measurement and setting theallowance error range so as to be narrower (e.g., plus or minus 3% ofthe middle value).

In response to a distinguished command to be inputted via aninput/output circuit 15, the microprocessor 7 allows the semiconductorlight-emitting devices 2, 3 a and 3 b, via the projector circuits 10, 11a and 11 b, to light up in the form of pulses for a predetermined shorttime, while reading, via the light receiving circuit 13 and A/Dconverting circuit 14, the reference value and detecting value which aresuccessively outputted from the light receiving device 5 insynchronization therewith.

Then the microprocessor 7 divides the first and second detecting valuesby the reference value, to obtain first and second computed values, andperforms identification based on the first and second computed valuesand the stored data of the storage part 6, and then outputs the resultof identification to the exterior via the input/output circuit 15.

The operation of this identification will be described in detail. Whenthe first computed value is not in the range of 48.07 to 48.22, it isjudged to which middle value in a plurality of middle valuescorresponding to the respective plastics shown in Table 1 the firstcomputed value is the closest. Thereby, it is judged by which plastic inthe above-mentioned plural types of plastics the object to be identified4 is formed. Alternatively, as a modification of this case, the judgmentof type may be performed by judging within which allowance error rangein the plural allowance error ranges corresponding to the respectiveplastics shown in Table 1 the first computed value falls.

On the other hand, when the first computed value is in the range of48.07 to 48.22, it is judged to which of the middle value correspondingto PVC (77.23) and the middle value corresponding to PS (35.92) shown inTable 2 the first detecting value is closer. Thereby, it is judged bywhich of PVC and PS the object to be identified 7 is formed.Alternatively, as a modification of this case, it is judged within whichof the allowance error range corresponding to PVC (73.37 to 81.09) andthe allowance error range corresponding to PS (34.12 to 37.72) thesecond detecting value falls. Thereby, it is judged by which of PVC andPS the object to be identified 7 is formed.

As described above, according to this preferred embodiment, thefollowing effects are obtainable in addition to the effects according tothe first preferred embodiment.

That is, according to this preferred embodiment, identification isperformed by using the second detecting light L2 b of which wavelengthis in the range of 1640 to 1700 nm, besides the first detecting light L2a of which wavelength is in the range of 1700 to 1760 nm. Therefore,when in the wavelength band of the first detecting light L2 a, the lightabsorptance of plural plastics (hereat, PVC and PS) are alike to make itdifficult to perform accurate identification merely by the firstdetecting light L2 a, such plastics can be identified accurately byusing the second detecting light L2 b.

Modifications

Modification of the plastic identifying apparatus 1 and 21 (particularlythe plastic identifying apparatus 21) of the foregoing first and secondpreferred embodiments will next be described based on FIG. 13. In theforegoing plastic identifying apparatus 21 and the like, thesemiconductor light-emitting devices 2, 3 a and 3 b are arranged tosuccessively light up, whereas in a plastic identifying apparatus 31according to this modification, there are disposed light receivingdevices 5 a, 5 b and 5 c so as to correspond to semiconductorlight-emitting devices 2, 3 a and 3 b, respectively, and thesemiconductor light-emitting devices 2, 3 a and 3 b are arranged tolight up at the same time.

In the construction of FIG. 13, first and second dichroic mirrors 32 and33 are disposed on a light receiving optical path at the back of a lightreceiving lens 12. A reference light L1, after passing through an objectto be identified 4 to the apparatus 31 via the light receiving lens 12,passes through the two dichroic mirrors 32 and 33 and is received by alight receiving device 5 a. Similarly, a first detecting light L2 aentered into the apparatus 31 via the light receiving lens 12 passesthrough the first dichroic mirror 32 and is reflected from the seconddichroic mirror 33 and received by a light receiving device 5 b.Similarly, a second detecting light L2 b entered into the apparatus 31via the light receiving lens 12 is reflected from the first dichroicmirror 32 and received by a light receiving device 5 c. The outputsignals outputted from the light receiving devices 5 a to 5 c areinputted to a microprocessor 7 via light receiving circuits 13 a to 13 cand A/D converting circuits 14 a to 14 c, which are disposed so as tocorrespond to the light receiving devices 5 a to 5 c, respectively. Ifrequired, dichroic mirrors that respectively correspond to thewavelengths of the reference light L1 and the detecting lights L2 a andL2 b, are disposed in the light receiving devices 5 a, 5 b and 5 b.

Although the examples shown in FIGS. 11 to 13 show the case that theplastic identifying apparatuses 1, 21 or 31 is integrally constructedinto one unit, the plastic identifying apparatuses 1, 21 or 31 may beconstructed separately into plural (e.g., two) units, such as aprojector unit and a light receiving unit. In this case, for example,the projector unit is provided with projector devices 2, 3, 3 a, 3 b,projector circuits 10, 11, 11 a, 11 b, and dichroic mirrors 8, 22, andlens 9 in the components shown in the identifying apparatuses 1, 21 or31, and the light receiving unit is provided with components other thanthese components in the components shown in the identifying apparatuses1, 21 or 31.

Other modifications of the plastic identifying apparatuses 1 and 21according to the foregoing first and second preferred embodiments willnext be described based on FIGS. 14 and 15. The foregoing plasticidentifying apparatuses 1 and 21 employ a transmission type opticalsystem, whereas plastic identifying apparatuses 41 and 51 according tothe modifications of FIGS. 14 and 15 employ a reflection type opticalsystem.

Specifically, in the plastic identifying apparatus 41, a half mirror 42is disposed on the optical path between a dichroic mirror 8 and a lens9, and the reflected lights of a reference light L1 and detecting lightL2 from an object to be identified 4, which have been irradiated to theobject to be identified 4 via the half mirror 42 and lens 9, arereceived via the lens 9 and reflected from the half mirror 42 and thenreceived by a light receiving device 5. In the plastic identifyingapparatus 51, a half mirror 42 is disposed on the optical path between adichroic mirror 22 and a lens 9.

When light is irradiated to an object to be identified 4, part of thelight is reflected from the surface of the object to be identified 4while the rest enters the interior of the object to be identified 4.Part of the entered light is absorbed by the object to be identified 4and the rest passes through the object to be identified 4,alternatively, it is reflected due to scattering in the interior of theobject to be identified 4. Accordingly, the quantity of light of thereflected light from the object to be identified 4 that is obtained whenan irradiation light of a predetermined wavelength and a predeterminedquantity of light is irradiated to the object to be identified, varieswith the rate that the object to be identified 4 absorbs the irradiationlight according to the wavelength of the irradiation light. It istherefore possible to identify plastics based on the quantity of lightof the reflected light from the object to be identified 4.

Although the plastic identifying apparatus 41 employs a coaxial opticalsystem in which the optical axis of the irradiation light toward theobject to be identified 4 and the optical axis of the reflected lightreceived from the object to be identified 4 are set on the same axis, itmay employ a different-axial optical system in which the optical axis ofthe irradiation light and the optical axis of the reflected light areset on different axes.

In the forgoing first and second preferred embodiments, the correctionof each detecting value is made by dividing each detecting value by thereference value. As a still another modification, the correction of eachdetecting value may be made by obtaining a difference between eachdetecting value and the reference value.

In the foregoing second preferred embodiment, the plastic identificationis conducted by using two detecting lights L2 a and L2 b. As a stillanother modification, the plastic identification may be conducted byusing three or more detecting lights that respectively have thewavelengths corresponding to the absorption wavelength bands of theabove-mentioned plastics.

Although in the foregoing first and second preferred embodiments,identification is conducted with respect to seven types of plastics, itmay be arranged so as to identify in an alternative fashion, namely,whether an object to be identified 4 is formed by PET or other type ofplastic.

In connection with this point, in the wavelength range of 1700 to 1760nm, the light absorptance of PET translates at a low level, whereasHDPE, PVC, LDPE, PP and PVDC holds its absorption wavelength band. Inthe range of 1640 to 1700 nm, PET and PS holds its absorption wavelengthband, and the light absorptance of PS translates at a higher level thanPET, and the light absorptance of the plastics of HDPE, PVC, LDPE, PPand PVDC translates at a low level. Therefore, by using a detectinglight of which wavelength is in the range of 1700 to 1760 nm or 1640 to1700 nm, PET can be easily and accurately identified from otherplastics.

Although in the foregoing first and second preferred embodiments, it isconstructed so as to perform only plastic identification, a color sensorfor optically detecting the color of the object to be identified 4 maybe added to perform plastic identification and color detection at thesame time. Thereby, plastic identification and color detection can beconducted by one apparatus.

Although in the foregoing first and second preferred embodiments, thecoaxial optical system in which the reference light L1 and the detectinglights L2, L2 a and L2 b are irradiated on the same axis, thedifferent-axial optical system may be employed.

As a still other modification of the plastic identifying apparatuses 1,21 and 31 shown in FIGS. 11 to 13, an optical fiber is interposed on theoptical path between the projector lens 9 and light receiving lens 12,and the object to be identified 4, the irradiation light and transmittedlight on the optical path therebetween may be transferred by the opticalfiber.

As a still other modification of the plastic identifying apparatuses 41and 51 shown in FIGS. 14 and 15, an optical fiber is interposed on theoptical path between the projector lens 9 and the object to beidentified 4, the irradiation light and transmitted light on the opticalpath therebetween may be transferred by the optical fiber.

As a modification of the plastic identifying apparatuses 1, 21, 31, 41and 51 shown in FIGS. 11 to 15, the light of which wavelength is in therange of 1500 to 1760 nm may be used as the reference light L1. In thiscase, when the wavelength of the reference light L1 exceeds 1640 nm, itmay be suitably changed according to the situation as to which light ofthe above-mentioned plural lights that the light source irradiates (L1,L2, L2 a, L2 b) should be used for the reference light L1 or thedetecting light L2, L2 a, L2 b.

Note that according to the plastic identifying apparatuses 1, 21, 31, 41and 51 according to the foregoing preferred embodiments andmodifications, not only existing plastics such as the mentioned sevenplastics, but new plastics to be made in the future can be identified.

While the preferred embodiments of the invention has been described, itis to be understood that the scope of the invention is not limited tothe foregoing preferred embodiments but defined by the accompanyingclaims.

What is claimed is:
 1. A plastic identifying apparatus (1, 21, 31, 41,51) to identify by what type of plastic in predetermined plural types anobject made of plastic to be identified (4) is formed, characterized bycomprising: a light source (2, 3, 3 a, 3 b) irradiating to said objectto be identified a detecting light (L2, L2 a, L2 b) of which wavelengthis in an absorption wavelength band to increase the light absorptance ofat least one type plastic in said plural types, and a reference light(L1) of which wavelength is different from said wavelength of saiddetecting light; a light receiving means (5, 5 a, 5 b, 5 c) receiving atransmitted light or reflected light of said reference light and saiddetecting light from said object to be identified, and outputting areference value expressing the quantity of light received of saidreference light and a detecting value expressing the quantity of lightreceived of said detecting light; and an identifying means (7) computinga proportion of or difference between said reference value and saiddetecting value, and identifying, based on the computed value, by whattype of plastic in said plural types said object to be identified isformed.
 2. The plastic identifying apparatus according to claim 1,characterized in that said light source comprises: a first semiconductorlight-emitting device (2) emitting said reference light; and a secondsemiconductor light-emitting device (3) emitting said detecting light.3. The plastic identifying apparatus according to claim 2, characterizedin that said first semiconductor light-emitting device and said secondsemiconductor light-emitting devices are respectively formed by a laserdiode.
 4. The plastic identifying apparatus according to claim 2,characterized in that said first semiconductor light-emitting device andsaid second semiconductor light-emitting devices are respectively formedby a light emitting diode.
 5. The plastic identifying apparatusaccording to claim 1, further comprising a storing means (6) in whichplural reference values that respectively correspond to said pluraltypes of plastics are stored, characterized in that: said identifyingmeans identifies that said object to be identified is formed by plasticof the type corresponding to said reference value closest to saidcomputed value in said plural reference values stored in said storingmeans.
 6. The plastic identifying apparatus according to claim 1,characterized in that the wavelength of said reference light is in awavelength region in which the light absorptances of all the types ofplastics in said plural types are of substantially the lowest level. 7.The plastic identifying apparatus according to claim 1, characterized inthat the wavelength of said detecting light is in an infrared lightregion having a longer wavelength than 1600 nm.
 8. The plasticidentifying apparatus according to claim 1, characterized in that thewavelength of said detecting light is in the range of 1700 to 1760 nm or1640 to 1700 nm.
 9. The plastic identifying apparatus according to claim1, characterized in that the wavelength of said reference light is inthe range of 1500 to 1600 nm.
 10. The plastic identifying apparatusaccording to claim 1, characterized in that the wavelength of saidreference light is in the range of 1500 to 1760 nm.
 11. The plasticidentifying apparatus according to claim 8, characterized in that saididentifying means identifies, based on said computed value, by which ofpolyethylene terephthalate and other type of plastic said object to beidentified is formed.
 12. A plastic identifying apparatus (21, 31) toidentify by what type of plastic in predetermined plural types an objectmade of plastic to be identified (4) is formed, characterized bycomprising: a light source (2, 3 a, 3 b) irradiating to said object tobe identified plural detecting lights (L2 a, L2 b) and a reference light(L1) of which wavelength is different from the wavelengths of saiddetecting lights; a light receiving means (5, 5 a, 5 b, 5 c) receiving atransmitted light or reflected light of said reference light from saidobject to be identified, and a transmitted light or reflected light ofsaid detecting lights from said object to be identified, and outputtinga reference value expressing the quantity of light received of saidreference light and plural detecting values expressing the quantity oflight received of said detecting lights; and an identifying means (7)computing a proportion of or difference between said reference value andeach of said detecting values, and identifying, based on the computedvalue that said object to be identified is formed by what type ofplastic in said plural types, and in that: the wavelengths of saiddetecting lights are in an absorption wavelength band to increase thelight absorptance of at least one type of plastic of said plural typesand are different from each other.
 13. The plastic identifying apparatusaccording to claim 12, characterized in that the wavelength of saidreference light is in a wavelength region in which the lightabsorptances of all the types of plastics in said plural types are ofsubstantially the lowest level.
 14. The plastic identifying apparatusaccording to claim 12, characterized in that the wavelengths of saidplural detecting lights are in an infrared light region having a longerwavelength than 1600 nm.
 15. The plastic identifying apparatus accordingto claim 12, characterized in that said plural detecting lights thatsaid light source irradiates contains at least a first light of whichwavelength is in the range of 1700 to 1760 nm, and a second light ofwhich wavelength is in the range of 1640 to 1700 nm.
 16. The plasticidentifying apparatus according to claim 12, characterized in that thewavelength of said reference light is in the range of 1500 to 1600 nm.17. The plastic identifying apparatus according to claim 12,characterized in that the wavelength of said reference light is in therange of 1500 to 1760 nm.
 18. A plastic identifying apparatus (1, 21,31, 41, 51) to identify by what type of plastic in predetermined pluraltypes an object made of plastic to be identified (4) is formed,characterized by comprising: a light source (2, 3, 3 a, 3 b) capable ofirradiating plural lights (L1, L2, L2 a, L2 b) of which wavelengths arein an absorption wavelength band to increase the light absorptance of atleast one type of plastic in said plural types and are different fromeach other, and irradiating one of said plural lights as a referencelight (L1) to said object to be identified and irradiating at least onelight of the rest in said plural lights as a detecting light (L2, L2 a,L2 b) to said object to be identified; a light receiving means (5, 5 a,5 b, 5 c) receiving a transmitted light or reflected light of saidreference light and said detecting light from said object to beidentified, and outputting a reference value expressing the quantity oflight received of said reference light and a detecting value expressingthe quantity of light received of said detecting light; and anidentifying means (7) computing a proportion of or difference betweensaid reference value and said detecting value, and identifying, based onthe computed value, by what type of plastic in said plural types saidobject to be identified is formed.
 19. The plastic identifying apparatusaccording to claim 18, characterized in that it is changeable as towhich light of said plural lights irradiated by said light source isused as said reference light or said detecting light.
 20. A plasticidentifying method of identifying by what type of plastic inpredetermined plural types an object made of plastic to be identified(4) is formed, characterized by comprising the steps of: a lightirradiating step of irradiating to said object to be identified, by apredetermined light source (2, 3, 3 a, 3 b), a detecting light (L2, L2a, L2 b) of which wavelength is in an absorption wavelength band toincrease the light absorptance of at least one type of plastic in saidplural types, and a reference light (L1) of which wavelength isdifferent from said wavelength of said detecting light; a lightreceiving step of receiving by a predetermined light receiving means (5,5 a, 5 b, 5 c) a transmitted light or reflected light of said referencelight and said detecting light from said object to be identified, andoutputting to said light receiving means a reference value expressingthe quantity of light received of said reference light and a detectingvalue expressing the quantity of light received of said detecting light;and an identifying step of computing a proportion of or differencebetween said reference value and said detecting value, and identifying,based on the computed value, by what type of plastic in said pluraltypes said object to be identified is formed.
 21. A plastic identifyingmethod of identifying by what type of plastic in predetermined pluraltypes an object made of plastic to be identified (4) is formed,characterized by comprising the steps of: a light irradiating step ofirradiating to said object to be identified, by a predetermined lightsource (2, 3 a, 3 b), plural detecting lights (L2 a, L2 b) of whichwavelengths are in an absorption wavelength band to increase the lightabsorptance of at least one type plastic in said plural types, and areference light (L1) of which wavelength is different from saidwavelengths of said detecting lights; a light receiving step ofreceiving by a predetermined light receiving means (5, 5 a, 5 b, 5 c) atransmitted light or reflected light of said reference light and saiddetecting lights from said object to be identified, and outputting tosaid light receiving means a reference value expressing the quantity oflight received of said reference light and plural detecting valuesexpressing the quantity of light received of said detecting lights; andan identifying step of computing a proportion of or difference betweensaid reference value and each of said detecting values, and identifying,based on the computed value, by what type of plastic in said pluraltypes said object to be identified is formed.